The present invention relates to a radiation-sensitive composition which comprises:
(a) a polymeric binder which is insoluble in water and soluble in aqueous-alkaline solutions;
(b) a compound which forms a strong acid under the action of actinic radiation; and
(c) a compound which has at least onne C--O--C bond which can be split by acid, and which is suitable for use in the production of printing plates and photoresists.
Positive-working photosensitive compositions, i.e., compositions which comprise the above-mentioned constituents and are used to prepare photosensitive coatings which are rendered soluble in the exposed areas are known in the art.
The vast majority of these compositions contain phenolformaldehyde condensation products, particularly novolaks, as alkali-soluble binders. Other alkali-soluble binders which can be used and which are mentioned, for example, in German Pat. No. 2,718,254, include copolymers of maleic anhydride and styrene, copolymers of vinyl acetate and crotonic acid, copolymers of methyl methacrylate and methacrylic acid, and novolaks which have been modified by chloroacetic acid. For various well-known reasons, these copolymers are not preferred in the art. Virtually all known commercial products, therefore, contain novolaks. Novolaks used as binders, however, also have disadvantages for particular applications.
Due to the chemical constitution and the low molecular weight of novolak resins, which is predetermined by synthesis, these layers are relatively brittle. Accordingly, fractures of the layer often occur in the processing thereof, for example, when exposing the layer in contact with a mask or when laminating the layer as a dry resist to a support surface. This characteristic has a particularly adverse effect in the case of the relatively greater layer thicknesses which are preferred for dry resist materials.
In European Patent Application No. 0,042,562 a corresponding photosensitive composition is described which comprises, in addition to the alkali-soluble binder, another polymer, for example, a polyurethane, a polyvinyl alkylether, a polyalkylacrylate, or a hydrogenated colophony derivative, in order to increase the flexibility of the layer and improve other properties. But by adding these resins, which display the solubility behavior unlike that of novolaks, other properties, for example, developability, resistance of the printing stencils to acid or alkali are adversely influenced.
Other positive-working photosensitive compositions are known which contain o-quinone-diazides and novolaks. These compositions, which are widely used in the production of lithographic printing plates, also form relatively brittle layers. These photosensitive systems have also been combined with other alkali-soluble compounds in an attempt to modify particular properties. German Pat. No. 2,322,230, for example, describes a combination of different photosensitive compounds, for example, of o-naphthoquinone diazides, with polyvinyl phenols. The printing plates thus obtained have the advantages of an increased print run and an improved etch resistance. It is mentioned in the specification of the aforementioned German patent that plasticizers can be added to the layer, as is similarly done in the case of layers containing novolaks. To date, even these materials have not been adopted in practice.
The compositions comprising o-quinone diazides as photosensitive compounds have the disadvantage of a clearly lower photosensitivity, as compared with compositions comprising the above-mentioned compounds which can be split by acid. This has an unfavorable effect, particularly in applications requiring higher layer thicknesses, for example, in the dry resist process.